Field of the Invention
Aspects of the present invention relate generally to mobile communications, and more particularly, to methods and devices for DRX paging cycle extension of user equipment (UE) in IDLE mode.
Description of the Related Art
To receive paging messages from an evolved universal terrestrial radio access network (E-UTRAN), the user equipment (UE) in an IDLE mode monitors the physical downlink control channel (PDCCH) for using a Paging Radio Network Temporary Identifier (P-RNTI) to indicate paging. The UE only needs to monitor the PDCCH channel at certain UE-specific occasions, i.e., at specific subframes within specific frames. At other times, the UE may apply discontinuous reception (DRX) not to listen to the paging messages, meaning that the UE can turn off its receiver to save battery power.
Each cell broadcasts a default paging cycle, so that the E-URTAN can configure the radio frames and subframes used for paging. In addition, upper layers may use dedicated signaling to configure a UE-specific paging cycle. If the default paging cycle and the UE-specific paging cycle are both configured, the UE applies the lowest value of the above two as the paging cycle. The UE would calculate a radio frame (a Paging Frame (PF)) and a subframe within that PF (a paging occasion (PO)), which E-URTAN uses to page the UE. One Paging Occasion (PO) is a subframe, which is an occasion of the P-RNTI transmitted on the PDCCH used to send the paging message. One Paging Frame (PF) is a Radio Frame, which may comprise one or multiple paging occasions. When the DRX is used, the UE only needs to monitor one PO for itself per DRX cycle.
The PF and PO are determined by using the DRX parameters provided in System Information (SI) and the following equation, wherein the PF is given by following equation:SFN Mod T=(T div N)*(UE_ID Mod N).  (1)
Wherein Mod represents modulo operation and div represents division operation. T represents the paging cycle, and UE_ID represents the ID of the UE (i.e., a terminal identification). N=min(T, nB), wherein nB represents the number of paging subframes per frame*T.
The index i_s can be derived from the following equation:i_s=floor(UE_ID/N)mod Ns.  (2)
Wherein floor represents a floor function returning an integer portion of a number, and Ns=max(1, nB/T). The PO can be obtained from the following mapping relationship according to i_s and the parameter Ns, which may be found in TABLE 1 and TABLE 2. TABLE 2 shows that the parameters can be applied to all TDD UL/DL configurations:
TABLE 1the corresponding relationshipamong PO, i_s and Ns in FDD modePO whenPO whenPO whenPO whenNsi_s = 0i_s = 1i_s = 2i_s = 319N/AN/AN/A249N/AN/A40459
TABLE 2the corresponding relationshipamong PO, i_s and Ns in TDD modePO whenPO whenPO whenPO whenNsi_s = 0i_s = 1i_s = 2i_s = 310N/AN/AN/A205N/AN/A40156
Once DRX parameter values are changed in the SI, the DRX parameters stored in the SI shall be updated locally in the UE. If the UE has no international mobile subscriber identity (IMSI). For example, when the UE makes an emergency call without using the universal subscriber identity module (USIM), the UE may use the default identity UE_ID=0 in the equation (2) described above.
The following parameters are used to calculate PF and i_s. T is the DRX cycle of the UE, and T is determined by the minimum value between the UE specific DRX cycle value (obtained through the upper layer configuration) and the default DRX cycle value (obtained by broadcasting the SI). If the UE specific DRX cycle is not configured by the upper layer, the default DRX cycle value is used. nB is one of the set {4T, 2T, T, T/2, T/4, T/8, T/16, T/32}. N=min(T, nB), Ns=max(1, nB/T), UE_ID=IMSI mod 1024. IMSI is given as an integer sequence of 10 digits. IMSI may be a decimal integer in the equation described above, wherein the first digit given in the integer sequence represents the highest order digit. For example: IMSI=12 (digit1=1, digit2=2).
However, for UEs of certain traffics, such as machine type communication (MTC) UE, due to the traffic characteristics with small packets and small amount of data, there is no need to monitor PDCCH under the current mechanism. Since there is not so much data needed to interact with the eNB in real-time, the mobile terminals need low power consumption. However, the mobile terminals are generally in an IDLE mode most of the time. Thus, there is a need for power saving schemes for mobile terminals in the IDLE mode.